1. Field of the Invention
The present invention relates to a target used for measuring the three-dimensional shape of an object to be measured, and also to a three-dimensional-shape measurement device using the target.
2. Description of the Related Art
A laser scanner is a well-known example of three-dimensional-shape measurement device used for acquiring, in a short period of time, data on the three-dimensional shape (3-D data) of an object to be measured (hereinafter also referred to as “to-be-measured object”).
FIG. 1 illustrates an example of measuring a to-be-measured object by a laser scanner. FIG. 1 shows a to-be-measured object 100 (e.g. a building as a physical structure). For acquiring data on the three-dimensional shape of the to-be-measured object 100, a laser scanner 101 is set, for example, at a reference point R1, scans a scan area E1, and acquires point-cloud data for the scan area E1.
Then, the laser scanner 101 is set, for example, at a reference point R2, scans, for example, a scan area E2, and acquires point-cloud data for the scan area E2. As has been described above, scan areas are appropriately set depending on the three-dimensional shape of the to-be-measured object 100, and the laser scanner 101 acquires point-cloud data for each scan area by scanning repeatedly a number of times as many as the scan areas. Here, the scan areas of the to-be-measured object 100 overlap one another, and targets 103 for the measurement of three-dimensional shape are placed in each overlapped portion. The point-cloud data for all the scan areas are combined on the basis of reference points defined by the target 103, and thus data on the three-dimensional shape of the to-be-measured object 100 is acquired. The three-dimensional shape data thus acquired sometimes are converted into the public survey coordinates.
For the purpose of acquiring the coordinates of the center as a reference point, the target 103 used together with the laser scanner 101 is configured, as shown in FIG. 2, such that: a circular central region 103a has the highest reflectivity; a circular peripheral region 103b surrounding the circular central region 103a has the lowest reflectivity; and a reflective region 103d located between a rectangular frame 103c and the circular peripheral region 103b has an intermediate reflectivity.
Incidentally, it is known that the target 103 may be also configured such that: the reflective region 103d located between the rectangular frame 103c and the circular peripheral region 103b has the highest reflectivity; the circular peripheral region 103b has the lowest reflectivity; and the circular central region 103a has the intermediate reflectivity (reference to U.S. Pat. No. 6,804,380B1, for example).